Field of the Invention
The invention lies in the field of environmental technology. Specifically, the invention relates to a method for the decontamination of soil and mud or sludge of any kind which are contaminated with hazardous substances and petroleum products.
The ever increasing environmental awareness has produced more stringent laws and regulations for the protection of human and animal health. At least in the developed countries it is no longer tolerated for contaminated soil to be deposited in open landfills, while special deposit sites for hazardous waste are limited and expensive. Therefore, a worldwide search is under way for new and improved technologies that provide better, faster and less expensive environmental clean up of contaminated sites and materials.
For a time it was common practice to burn or bury contaminants (the latter after the hazardous material concentrates had been encapsuled in cement or glass). One example is in situ vitrification, where metals are at 1600.degree. C. capsuled in molten silicate structures. In recent years other technologies have been increasingly applied, for instance technologies based on biological in situ and ex situ activities, where microorganisms are introduced into the soil to create chemical and/or physical activities, the end product is typically CO.sub.2 and H.sub.2 O.
There are other chemical methods (hazardous materials are converted to less dangerous materials, typically by reduction and sometimes also by oxidation), and extraction of hazardous materials by means of solvents.
In situ flushing operations wash away contaminated areas in the soil or in the groundwater with large amounts of water (provided the flushing water can be isolated and separated efficiently). Instead of using water, it is also possible to separate volatile organic substances from soil with (hot) steam. However, this requires an after-treatment of the extracted materials.
Washing of contaminated soil is conventional. Water can cleanse contaminating substances from soil, gravel and rocks mechanically. Water also may separate fine-grained particles (silt and clay) from coarse-grained particles (sand and gravel). In this case the water is loaded with the contaminants from the soil and needs to be treated adequately, before it can be reused or returned to surface and ground water.
To improve the cleaning power of water it has been suggested (German Patent Application DE 195 23007 A1; Duro Galvanit Chemie) to add detergents and have the water stream through the tank upwards. Surface active detergent should preferably be added. It is claimed that the upwardly streaming water creates--at adequate stream velocity--a layer of solid material. Multi-step washing procedures and continuously or intermittently draining of some of the wash water are the to complete the process of soil washing. They also imply however, that besides chemical additives (detergents) several steps of washing are necessary, thus this washing process takes up a considerable amount of time.
Likewise chemical additives shall be applied to the wash water for soil washing according to Ansaldo Volund A/S (Published International Application WO 98/082). There, additives are suggested which stabilize chemically the materials to be treated using a solution containing ferrous ions which allows the formation of stabilizing ferric oxides on the materials. The oxidized material is then heat-treated, at various temperatures (0.degree. C. to 1300.degree. C.), and carried out in several steps, in a furnace for obtaining melting or sintering with other products. The wash water is then oxidized, its pH regulated, and finally discharged. Supplementary, also embedding in concrete and covering with other solid materials are recommended. That prior art method is complex, time consuming and expensive. This is not to say that it does not have its proper place cleanup processes in which, due to the quantity and form of the contaminants in the soil and mud, several processes and technologies need to be combined in order to achieve the desired cleanup. This renders soil remediation expensive and time consuming. These facts impede the realization of ambitious endeavors such as those published in "Cleaning Up the Nation's Waste Sites" (U.S. Environmental Protection Agency; EPA 542-R-96-005A /1996 Edition). According to that text, the next 20 to 30 years will see a commitment of several billion dollars annually for the clean-up of sites contaminated with hazardous waste and petroleum products.